It might make a difference if they were 'hidden' or 'deleted' after you transferred them to your USB data storage. You're not clear about what exactly you did.
But, yes, I think he could have made a copy of your hard disk in an hour, to get the files off later.
recently i went to a technician. my power receiver was broken. i wanted to stay there,he told me to come after 3hrs. after wandering 1hr outside, i went to his shop. he already fixed my laptop within that time. before going to the shop,i transferred my private files to an usb data storage. now judging his overall attitude and everything, I am little bit concerning about my deleted(transferred) files. my question is, it is possible for someone to recover files within 1hour? i had only 120gb free space of my 300gb hard drive. and all my files were hidden ones. waiting for reply from someone expert on this field. thanks.